Wide Field Scorpion

[Volans]

G'day All,

I took this image of Scorpius while it was almost at the zenith. The details of the image follow. I don't have any tracking ability so bearing that in mind, can anyone suggest any improvements?

Peter.

Shooting Date/Time
4/05/2006 3:08:46 AM
Manual Exposure
Shutter Speed
3.2
Aperture
3.5
ISO Speed
800
Lens
18.0 - 55.0mm
Focal Length
18.0mm
White Balance Mode
Auto
Noise Reduction
On

[iceman (Mike)]

More exposure, Peter!

You can go for 15 seconds without tracking before you get star trails. You'll get a lot more detail in 15 seconds than in 3.2 seconds. I used to take several 15 second non-tracked images with my old Sony DSCP100, and they came out ok.

You should also take many shots and stack them in registar, registax or other programs (IRIS etc).

[[1ponders] (Paul)]

Hi Peter.

To work out your exposure time without star trails divide 700 by your FL when shooting at around 0 deg dec and 1000 close to the pole.

So at 18mm you could have gone around 35 sec (if you can do that on your camera). For 50mm around 15 sec. Some will say you can only divide 500 by the focal length. If you are doing large format then maybe but for what you are doing 700 will not be a problem.

[Volans]

Thanks for the advice Mike and Paul! But I am a touch confused. Effectively, you are both advocating longer exposures and I did do this on the same night and the result is below. Ok, I'll admit that the ISO was far less, 200 instead of 800 (pls don't ask what I was doing at 200 because I've no idea myself!) BUT, surely if the ISO is less then simply the result will be darker? And if it does have an affect on trails can you please explain to me how it does.

So why do I have trails with a 15 second exposure?

Shooting Date/Time
4/05/2006 3:06:06 AM
Shutter Speed
15
Aperture
3.5
ISO Speed
200
Lens
18.0 - 55.0mm
Focal Length
18.0mm

[[1ponders] (Paul)]

They are not "star trails" Peter. That is camera movement. The trail are not straight (for that short an exposure, longer exposures they are curved), they are far too long for 15sec. and there is a "bump" in the middle. I would guess a gust of wind, tripod movement or someone walking near the tripod during the exposure.

If I had to take one guess I would say the camera was moving downward under the force of gravity somehow. Either the tripod was settling, the camera mount wasn't tight of someone stepped near a leg particularly if it was on grass or a timber surface, but can happen on concrete as well but not usually at that FL unless its "wobbly" concrete

[RB (Andrew)]

Peter which camera are you using?

I'd stick to 800 ISO or try 1600 ISO in combination with longer exposure.
Stacking multiple images will help tremendously and this can also be done in Photoshop.

I had a little go at your first image to see if the detail can be increased.
Just boosted the levels and adjusted the curves in photoshop.

Cheers

[Volans]

Originally Posted by [1ponders]

They are not "star trails" Peter. That is camera movement. If I had to take one guess I would say the camera was moving downward under the force of gravity somehow.

Ahh Paul....well done and I should have realised myself. For a start the trails are going in the wrong direction for Earthly rotation now that I look at it. And the idea of the camera slowly tiliting downwards makes sense... operator error strikes again!! I guess I simply did not tighten the tripod head enough. That image was taken with the tripod sitting on the pavers around the pool.

Ok...now that has been cleared up... I'll have a crack at those longer exposures.

Thanks for the fiddle RB The stars are certainly much more defined and I can make out M7 alot more clearly!

Peter.

[iceman (Mike)]

What Paul said

You should also consider getting a wireless (or wired) remote, and use mirror-lockup.

I use the wireless remote from ebay ($20), and that way I avoid camera shake when pressing the shutter. And yeh, make sure your tripod doesn't move.

[middy]

..... or if you don't have a remote shutter release, you can use the self timer function on the camera where it counts down for 10 secs before taking the photo. That way you are not touching the camera when it takes the image.